EP0095440B1 - Hip joint prosthesis without collar - Google Patents

Description

The invention relates to a collarless hip joint prosthesis of the type specified in the preamble of claim 1 for cementless anchoring.

Since there have been certain disadvantages in the past when using bone cement, e.g. Loosening, have shown, efforts are made to attach endoprostheses without using bone cement if possible. However, there are also a number of difficulties. If, for example, the femoral part, which is used to hold the joint head, has a “collar”, the force is applied to the bones exclusively in the area of the “projecting” part. However, since the forces occurring in these conditions in a narrowly limited range are relatively large under load, the resulting “wobbling movements” can lead to loosening of the prosthesis socket.

Collarless prostheses have also become known which have a taper and wedge in the drilled medullary cavity. Such a prosthesis is described, for example, in EP-A 0 027 159. The disadvantage of these prostheses is that the wedge effect caused by the tapering of the prosthesis shaft in the distal part is very large, so that the stress on the bones in the radial direction is considerable under load and there is a risk of crack formation in particular in the case of osteoporotic bone.

Because of the complicated course of the widening areas in the outermost proximal area of the shaft, it is very difficult, with exact dimensional accuracy and normal anatomical conditions, to adapt to the medullary cavity in such a way that a defined distribution of force occurs when the shaft is inserted. If the prosthesis only wears in this area, there is in turn more or less selective loading and the corresponding disadvantageous properties for the bone substance.

From EP-A 0 044 915 a shaft part of a collarless hip endoprosthesis has become known which has an elliptical cross-section, the wedging taking place in the region of the bend or curvature of the prosthesis shaft following the adam arch, so that comparatively small bending moments become effective when the prosthesis is loaded excessive stress on the bone tissue should be excluded. However, this prosthesis also has the disadvantage that it is difficult to adapt the medullary canal to the relatively complicated shape. In addition, the bone opening must have a large area so that the prosthesis can be used, because in particular the area of strong curvature with an elliptical cross section requires a larger opening than corresponds to the end cross section of the prosthesis close to the joint ball.

Furthermore, from DE-A 2851 598 a prosthesis of the type mentioned at the outset is known, in which the shaft has an S-shaped bend in the AP plane. This bend forms an adaptation to the natural course of the medullary canal at a relatively large distance from the neck and can therefore only be used on prostheses with a relatively large length of the shaft. Since the convex area corresponds to a corresponding concave area on the opposite side of the shaft, a firm jamming does not occur. An exclusively S-shaped structure is not very suitable for achieving a press fit.

The invention is based on the object of designing a hip joint prosthesis of the type mentioned at the outset in such a way that force can be applied over an extended area without selective loading on the one hand - but on the other hand excessive radial stresses in the femur area are avoided.

This object is achieved by a hip joint prosthesis with the features specified in the characterizing part of claim 1.

The invention is based on the knowledge that the medullary canal in the area of the minor trochanter, into which the additional unilaterally provided elevation of the shaft of the hip prosthesis according to the invention engages, enables force introduction which ensures a firm fit of the prosthesis with limited forces caused by wedge action. At the same time, an anti-rotation lock is guaranteed and thus prevents loosening due to forces directed transversely to the central axis. Stress forces are primarily introduced in an area below the elevation intended for insertion into the minor trochanter, which has an enlarged taper, while the task of the further distal shaft area preferably consists in the transfer of forces directed transversely to the longitudinal axis of the prosthesis. The point of reference for the resulting moments is also the part of the survey that is located in the small trochanter.

The enlargement of the cross section in the area of the maximum curvature of the prosthesis is preferably used to accommodate a bore for fixation, since an enlarged material cross section of the shaft is available here. In addition, there is a threaded hole for fixation in the area of the distal end. The shaft of the hip joint prosthesis according to the invention preferably consists of a titanium alloy or else of plastic reinforced with carbon fibers.

The prosthesis according to the invention thus fundamentally differs, for example, from a prosthesis known from DE-C2059381, in which a bore is provided on an extension of the collar. Here the approach is on the "back" of the area of relatively strong curvature or the bend. Anchoring in the minor trochanter is excluded.

The insertion of the prosthesis is facilitated by the fact that the cross-section of the shaft in the area of the one-sided elevation is adapted to the cross-section just below the end used to hold the joint ball due to the physiological design. The rounded cross section is flattened on both sides in this area, is ovoid, elliptical or oval.

With an appropriate design of the opening in the proximal end of the bone, the insertion can easily be achieved by first turning the shaft end by an angle of approximately 90 ° until the area of the one-sided elevation has passed the outer bone opening. When the area of the trochanter minor in the medullary canal is reached, the shaft is turned back accordingly, so that the shaft area with the largest cross section at the end near the joint ball fits into the opening, the shoulder being supported in the area of the trochanter minor. This ensures a secure fit of the prosthesis. Since the shaft can be made relatively short in the case of an anatomical design as a left or right prosthesis, no problems arise when inserting it, and the guiding into the appropriate angular position takes place “of its own accord”, since further insertion is only possible in the correct angular position .

According to preferred developments of the invention, the prosthesis additionally has a slight curvature in a plane perpendicular to the plane of greater curvature - as is known from DE-A 2 851 598, the center or centers of the radii of curvature being opposite one another on the one-sided elevation arranged side of the shaft.

• Fig. 1 die erfindungsgemässe Prothese von der Körperachse her gesehen, in der AP-Ebene dargestellt.
• Fig. 2 dieselbe Prothese von posterior her betrachtet (Zeichenebene ist die LM-Ebene) und
• Fig. 3 und 4 Querschnitte durch die erfindungsgemässe Prothese in zwei verschiedenen Schnittebenen gemäss Figur 2, wobei Figur 3 in bezug auf Figur 4 um 90° versetzt dargestellt ist. Die Zeichnung ist etwa im Massstab 1:1 gehalten.

Other advantageous developments are specified in the dependent claims. An embodiment of the invention is described in more detail below. Show it:

• Fig. 1 seen the prosthesis according to the invention from the body axis, shown in the AP plane.
• Fig. 2 the same prosthesis viewed from the posterior (drawing level is the LM level) and
• 3 and 4 cross sections through the prosthesis according to the invention in two different sectional planes according to Figure 2, wherein Figure 3 is shown offset by 90 ° with respect to Figure 4. The drawing is kept on a scale of 1: 1.

The prosthesis shaft 2 inserted into the medullary canal of the femur 1 has a curve in its maximum curvature plane (the plane of the illustration according to FIG. 2 is the LM plane) in which the curvature decreases from the proximal to the distal end. The proximal end carries an extension 3, which serves to receive a joint ball 4 (shown in broken lines).

The cross section of the prosthesis shaft is essentially rounded over its entire length, the proximal end just below the attachment 3 having a contour as shown in FIG. 3.

This contour can be addressed as oval or elliptical. This cross-section decreases continuously towards its distal end, the flattened cross-sectional shape being essentially retained, apart from the one-sided elevation to be described below. The cross-sectional axis with smaller dimensions is perpendicular to the LM plane, in which the main curvature of the prosthesis socket runs.

As can be seen from FIG. 1, the shaft has a further curvature with a larger radius, the center of which is essentially perpendicular to the plane in which the larger curvature runs - it serves to adapt to the special conditions of the left and right femur .

The prosthesis can consist of body-compatible metal alloys as well as corresponding carbon fiber reinforced plastics, the choice of material being made in such a way that sufficient strength is ensured.

The prosthesis according to the invention is provided with a one-sided elevation in the form of a shoulder 5, which follows the minor trochanter in its contour. In the longitudinal direction of the shaft 2 on the surface over the area of the shoulder, the contour runs in such a way that a corresponding boundary line extends from an area which forms a small angle with the central axis - corresponding to the normal taper - to the top of the elevation 5 into one Range passes over, which forms an enlarged angle with the central axis, the transition taking place continuously. This line forms the left outer boundary in FIG. 1 and runs essentially concave to the apex of the elevation 5 in the region of the bore 6. The shoulder 5 has a comb-like summit region in the region of its highest elevation, which extends in the circumferential direction. From the hinge end of the shaft, the shoulder-shaped elevation follows the cross-section with sharper rounded corner areas with enclosed, essentially flat surface parts according to FIG. 3, while the area adjoining the crest downwards - starting from that shown in FIG. 4 in the area of the bore 6 Profile - approaching an even fillet towards the end.

The cross-section in this area is shown in FIG. 4, it being evident that there is an approximation to the contour of the cross-section in the area of line 111-111 in FIG. 2, so that this cross-sectional area according to FIG. 4 can pass through an opening without difficulty, which allows the cross section according to Figure 3. All that is required is a rotation about the longitudinal axis through a predetermined angle of essentially 90 °. Since the contour of the shaft is rounded without steps, there is an almost automatic guidance when inserting it into the medullary canal.

The area of the reinforced material cross section of the shoulder 5 serves to receive a threaded bore 6 with which the shaft can be fixed in the selected position by means of a screw. This fixation forms an additional safeguard, since the shape of the prosthesis filling the minor trochanter ensures its stable fit. The bore 6 runs in the plane of the bend or curvature and is directed essentially perpendicular to the central axis of the shaft.

The area corresponding to the cross section shown in FIG. 4 intersects the shoulder 5 in the area of its highest elevation. Without this shoulder, the shaft curved near the joint (curvation) would continuously taper towards its other end. It would always have a greater extension in the plane of this curvature than perpendicular to it. The shoulder-shaped elevation is added to this basic structure and protrudes from the plane of the curvature, the (additional) pitch being less in the longitudinal direction of the shaft than in the circumferential direction. The shoulder thus forms an additional bulge of the prosthesis socket, which otherwise has an essentially even contour. The shoulder protrudes laterally in an area of the shaft which is arranged essentially in the middle of the inner curve of the more curved area.

The section according to FIG. 4 goes through the summit area (ridge line) of the elevation designed as shoulder 5. The (additional) shoulder increases the cross-section of the tapered shaft on one side in such a way that the direction of the greatest cross-sectional extension no longer runs here in the plane of curvature, but in a 90 ° direction to it (in FIG. 4, therefore, horizontally instead of vertically) 4 is already rotated by 90 ° with respect to FIG. 3). If the cross-section of the shaft according to FIG. 4 is to pass through the upper opening prepared for the prosthesis cross-section according to FIG. 3, the shaft must be rotated by 90 ° when inserting the area according to FIG to be able to take. During this turning to the normal position, the shoulder enters an extension of the external bone structure consisting of corticalis, which is referred to as the "trochanter minor". The shoulder literally looks like a peg corresponding to a one-sided bayonet catch. The dimensions of the shaft are adapted to the dimensions of the human femur.

A corresponding threaded hole is also provided in the region of the distal shaft end, which is indicated by the dashed hole 6 '. This hole runs in the lateral-medial direction, since this direction can be easily reached by the aiming device used during the implantation. The corresponding fixation screws cross the femur completely and are used for additional fixation of the shaft.

The prosthesis shown in FIGS. 1 to 4 is intended for use on the left. Because of the already asymmetrical and therefore different design for the left and right in the area of the trochanter minor, the curvature with a large radius shown in FIG. 1 and running in the AP plane with a large radius can also be adapted to the anatomical requirements in the left or right femur, so that an optimal fit is guaranteed.

The area of maximum force application in the prosthesis according to the invention lies in the surface area which widens from the distal end to the unilateral shoulder 5. The resulting wedge angle is dimensioned so that the radially directed forces are limited. The seat of the prosthesis and thus the introduction of vertical loading forces is distributed over such a large area that micro-movements causing bone resorption are excluded. The medullary opening need not be subjected to complicated shaping in a complex manner, since the prosthesis according to the invention makes use of the physiological conditions found.

The length of the prosthesis neck can - depending on the individual requirements - be varied during manufacture.

Claims (10)

1. Collarless artificial hip-joint intended for fixing without cement, having a shaft (2) which close to the end will receive the ball (4) of the joint has a change of direction formed by a bend or curve, and the rounded shaft cross-section in which the bend or curve occurs, has a smaller transverse dimension perpendicular to the lateral-medial plane than in that plane, characterised in that on the shaft (2) in the region of the curve or bend is a shoulder-like lump projecting on one side of the lateral-medial plane to provide support in the region of the lesser trochanter, the shoulder-like lump (5) having slopes which are smaller in the longitudinal direction of the shaft than in the transverse direction, the slopes being relative to the shape of the generally oval shaft which tapers uniformly with the bend or curve in the throat region.

2. Artificial hip-joint according to claim 1, characterised in that the shoulder-like lump (5) has a convex ridge line extending in the transverse direction, while the external contour extending in the longitudinal direction of the shaft up to the ridge line on both sides of the lump is of concave shape.

3. Artificial hip-joint according to one of the preceding claims, characterised in that the shaft (2), starting from its end for receiving the ball (4) of the joint, has a taper, so that the contour of the cross-section in the region of the shoulder-like lump (5) is matched to that region of maximum cross-section which is to be formed immediately next to the end which receives or forms the ball of the joint.

4. Artificial hip-joint according to claim 3, characterised in that the direction of the maximum dimension of the cross-sectional contour (Fig. 4) in the region of the shoulder-like lump (5), and the direction of the maximum dimension in the region of the maximum cross-section (Fig. 3), occurring directly next to the end which receives or forms the ball of the joint, seen in the axial direction of the prothesis, form an angle to each other.

5. Artificial hip-joint according to claim 4, characterised in that the directions of maximum dimension form straight lines which do not meet in space and lie substantially perpendicular to each other.

6. Artificial hip-joint according to claim 4 or 5, characterised in that the cross-sectional contour (Fig. 4) in the region of the shoulder-like lump (5) does not extend beyond the surface of the region of maximum cross-section (Fig. 3) which occurs immediately next to the end which receives or forms the ball of the joint, when placed congruently.

7. Artificial hip-joint according to one of the preceding claims, characterised in that the shoulder-like lump (5) has a bore (6) through it which is substantially perpendicular to the main axis and cuts through in the region of the lump parallel to the plane in which the bend or curve runs.

8. Artificial hip-joint according to one of the preceding claims, characterised in that a bore (6') is provided extending transverse to the longitudinal axis of the prothesis and close to the end remote from the connection for the ball of the joint.

9. Artificial hip-joint according to claim 8 characterised in that the bore (6) is threaded.

10. Artificial hip-joint according to one of the preceding claims, characterised in that the shaft (2) has a further, but less pronounced curve about a point forming the centre on the side opposite to the one-sided shoulder-like lump (5).

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